This invention generally relates to a retaining device for restraining movement between two parts of a medical instrument. More particularly, the present invention pertains to a retaining clip for axially restraining movement between a dilator and a sheath forming part of a sheath assembly.
Some types of medical procedures that require intervention into a patient""s blood vessel for purposes of accessing a desired site (e.g., carotid artery) so that a medical procedure can be carried out involve the use of a guiding sheath. Once in place within the patient""s vessel, various types of medical instrumentation (e.g., a balloon catheter) can be fed through a lumen in the sheath and positioned at the desired site.
To initially gain access to a particular site within a patient, a needle is used to puncture the patient""s skin and gain entry to a desired blood vessel. A guide wire is then inserted into a lumen in the needle and is fed into the blood vessel. The needle is removed, with the guide wire being left in place. The tip of a sheath assembly, which includes a sheath, is then placed over the guide wire and advanced to a position inside the blood vessel. The guide wire is then advanced within the blood vessel to the desired site, followed by advancement of the sheath assembly to the desired location. Once the sheath assembly is in place at the desired site, the sheath can be used to introduce and guide medical instrumentation to the desired site within the blood vessel.
However, because the sheath is typically used as a mechanism for guiding medical instrumentation into a blood vessel, the sheath possesses a relatively large diameter. Inserting this relatively large diameter sheath into the patient without any special provision could cause trauma, injury or other difficulties to the patent. To avoid such difficulties, the sheath assembly typically includes a tubular dilator that is generally coaxially disposed within the tubular sheath. The distal end of the dilator is tapered to a relatively small diameter and extends beyond the distal end of the tubular sheath which may be formed so that it is also slightly tapered. A smooth transition is thus presented between the tapered distal end of the dilator and the distal end of the sheath. The tapered distal end of the dilator allows the dilator/sheath assembly to be introduced into a patient""s vessel in a manner that gradually increases the size of the opening into the vessel so that the vessel can ultimately accommodate the larger sized sheath without causing potential trauma, injury or other difficulties to the patient.
To achieve the desired gradual increase in the size of the opening into the vessel, the smooth transition between the tapered distal end of the dilator and the distal end of the sheath must be maintained during the use of the dilator/sheath assembly. This necessitates that axial movement between the dilator and the sheath be restrained during use of the dilator/sheath assembly. If the dilator is axially retracted within the sheath, the relatively large and somewhat blunt end of the sheath will be exposed and could cause the aforementioned undesirable trauma or injury to the patient.
Various proposals have been made for devices adapted to be used in connection with medical instruments for securing two elongated members relative to one another in a way that inhibits relative axial movement. For example, U.S. Pat. No. 5,064,414 discloses a locking clip for placement between a dilator and sheath. Although this clip may be able to secure the dilator and sheath relative to one another to inhibit relative axial movement, the construction of the locking clip is somewhat complicated and requires that the sheath with which it is used possess tabs for engagement by the locking clip. Further, the disclosed locking clip does not lend itself to being easily removed so that the dilator can be withdrawn fro the sheath once the dilator/sheath assembly is properly positioned within the vessel.
U.S. Pat. No. 4,233,974 discloses a bridging member specifically adapted for use in a spinal needle assembly to prevent the obturator stylet from axially moving relative to the cannula. This bridging member, although possibly useful in the context of a spinal needle assembly, is not particularly well suited for use in other contexts such as a dilator/sheath assembly. For example, in the case of the disclosed spinal needle assembly, the aforementioned patent describes that it the obturator and the cannula must be secured to one another in a way that prevents rotational movement of the obturator relative to the stylet. In the case of a dilator/sheath assembly, similar concerns about prohibiting rotational movement between the dilator and the sheath may not exist. In fact, in at least some applications, the guiding sheath is connected to a housing containing a hemostatic valve that is operable by way of a rotatable cap. With this construction, any type of device for axially restraining the sheath and dilator relative to one another should be designed so that when the device is in use, the cap is still capable of being rotated to effect operation of the hemostatic valve. In addition, in the case of a dilator/sheath assembly used in the manner described above, a device for axially restraining relative movement between the sheath and dilator should be designed to permit access to the lumen in the dilator. The spinal needle assembly locking clip disclosed in the aforementioned U.S. Pat. No. 4,233,974 is also not particularly well suited for being easily positioned in place and then subsequently removed.
A need thus exists for a retaining device that can be used with, for example, a sheath/dilator assembly which requires rotation of a cap to effect operation of a hemostatic valve.
A need also exists for a dilator/sheath assembly retaining device that is relatively uncomplicated in construction, yet can be readily mounted in place and subsequently removed without significant difficulty.
According to one aspect of the invention, a sheath assembly includes a tubular dilator, a tubular sheath and a retaining device. The dilator has a tapered distal end and possesses a lumen, and is connected to a hub. The sheath has a distal end and possesses a lumen, and is the connected to a housing provided with a hemostatic valve and a rotatable cap that is operatively associated with the hemostatic valve for operating the valve upon rotation of the cap. The dilator extends through the hemostatic valve and through the lumen of the sheath, with the tapered distal end of the dilator extending beyond the distal end of the sheath. The retaining device includes a clip surrounding circumferential portions of the hub and the cap as well as portions of oppositely facing end surfaces of the hub and the cap to restrain axial movement between the hub and the cap. The clip also has an inner surface shaped to permit rotation of the cap to operate the hemostatic valve.
Another aspect of the invention involves a retaining device for axially restraining movement between a tubular sheath connected to a housing provided with a rotatable cap and a tubular dilator connected to a hub and extending through a lumen in the housing and the sheath. The retaining device includes a generally C-shaped clip having spaced apart circumferential ends defining a clearance opening that opens into an interior of the clip to permit the clip to be mounted in a partial circumferentially surrounding relationship on the hub of the dilator and the cap of the housing. The interior of the clip has a curved inner circumferential surface to permit rotation of the rotatable cap when the clip is mounted on the hub of the dilator and the cap of the housing. The interior of the clip has first and second axially spaced apart and inwardly directed ridges located at opposite axial portions of the curved inner circumferential surface for overlapping with portions of oppositely facing end surfaces of the cap and the hub when the clip is mounted on the hub and the cap. The clip also includes at least one laterally outwardly extending finger engaging tab positioned adjacent one of the circumferentially spaced apart ends of the clip to facilitate removal of the clip from the hub and cap. The clip is also provided with at least one circumferentially extending through slot communicating the inner surface of the clip with an outer surface of the clip to permit flexing of the clip during removal of the clip from the hub and cap.
In accordance with another aspect of the invention, a retaining device for restraining axial movement between a tubular sheath, connected to a housing having an enlarged part, and a tubular dilator, connected to a hub and extending through a lumen in the housing and the sheath, includes a clip having an interior bounded by an inner circumferential surface of the clip, with the clip having spaced apart circumferential ends between which is defined a clearance opening that opens into the interior of the clip for allowing the clip to be mounted on the hub and the enlarged part of the housing, and with the clip also having an opening at each axial end of the clip, the interior of the clip defining first and second interior portions positioned axially adjacent one another. The first interior portion is adapted to receive and circumferentially surround a portion of the hub while the second interior portion is adapted to receive and circumferentially surround a portion of the enlarged part of the housing, with the first and second interior portions of the clip being of different size.
According to a further aspect of the invention, a retaining device for restraining axial movement between a tubular sheath, connected to a housing having an enlarged part, and a tubular dilator, connected to a hub and extending through a lumen in the housing and the sheath, includes a clip having an interior bounded by an inner circumferential surface of the clip, with the clip having spaced apart circumferential ends defining a clearance opening that opens into the interior of the clip for allowing the interior of the clip to receive portions of the hub and the enlarged part of the housing, and with the clip including at least one laterally outwardly extending finger engaging tab extending laterally outwardly from adjacent one of the circumferential ends of the clip for being engaged by an individual""s finger to facilitate removal of the clip from the hub and the enlarged part of the housing.